1. Field of the Invention
The present invention relates in general to an ink-jet recording apparatus which performs recording or printing by ejecting ink droplets.
2. Discussion of Related Art
An ink-jet head of an ink-jet printer for ejecting ink droplets onto a recording medium such as a recording sheet includes: a flow-passage unit in which are formed nozzles through which ink droplets are ejected and pressure chambers which communicate with the nozzles; actuators which apply an ejection energy to ink in the pressure chambers; and a driver IC in which are incorporated signal output circuits which output drive signals for driving the actuators. As the actuators each configured to apply a pressure to the ink in the pressure chambers by changing the volume thereof, there is known one disclosed in Patent Document 1 including: a piezoelectric sheet (piezoelectric layer) extending over a plurality of pressure chambers; a plurality of individual electrodes facing respectively the plurality of pressure chambers; and a common electrode (ground electrode) which faces the plurality of individual electrodes via the piezoelectric sheet and to which a base potential is given. In the disclosed actuators, when a drive pulse signal outputted from the signal output circuit of the driver IC is inputted to one of the individual electrodes, an electric field is generated at a portion of the piezoelectric sheet interposed between the above-indicated one individual electrode and the common electrode in a thickness direction of the piezoelectric sheet, so that the piezoelectric sheet at that portion expands or elongates in the thickness direction. Accordingly, the volume of the pressure chamber that corresponds to the one individual electrode is changed, whereby the pressure (ejection energy) is given to the ink in that pressure chamber.
In the ink-jet printer, there may be a risk that a short circuit occurs in the driver IC or the actuators due to breakage thereof, causing an overcurrent to flow in the signal output circuits. In particular when the ink-jet printer is in a non-operating state or in a standby state, the short circuit occurs at high frequency due to occurrence of migration phenomenon and entry of the ink from the pressure chambers into the corresponding actuators. When the ink-jet printer is turned on with the short circuit occurring, the overcurrent flows in the signal output circuits. To monitor the overcurrent, an electric current detecting circuit may be provided for detecting an electric current from the power supply device. However, since a maximum value of the electric current consumed when all of the actuators of the printer are placed in a charged state upon startup of the printer is high, it is difficult to detect the overcurrent when the overcurrent flows only in the signal output circuits corresponding to a part of the actuators. In view of this, there has been disclosed, in Patent Document 2, for instance, a technique of monitoring the electric current in each signal output circuit by disposing the electric current detecting circuit for each of the signal output circuits corresponding to the actuators.    Patent Document 1 JP 2002-36568 (FIG. 1)    Patent Document 2 JP 2002-127405 (FIG. 1)